1. Field of the Invention
The present invention relates generally to magnetic levitation systems for moving objects, and more specifically, to an improved magnetic levitation train system.
2. Description of Related Art
Halbach arrays, invented by Klaus Halbach in the 1980s for use in particle accelerators, represent a maximally efficient way to arrange permanent-magnet material when it is desired to produce a strong periodic magnetic field adjacent to the array. The beauty of the concept is that the effect of the cross-magnetized magnet bars in the array is to enhance the periodic magnetic field at the front face of the array, while canceling it back face of the array. Not only is the field enhanced, but analysis shows that in a long array the horizontal and vertical components are nearly purely sinusoidal in their spatial variation, with negligible higher spatial harmonics. If the Halbach array is then fabricated from high-field permanent-magnet material, such as NdFeB, peak fields near the front face of the array of order 1.0 Tesla are possible.
Particularly for lower-speed applications of magnetic levitation, such as for urban train systems, it is desirable to employ systems that are simple in construction and operation and that have low drag at urban speeds. Conventional maglev systems, that is, ones employing superconducting coils, or ones requiring servo-controlled electromagnets for levitation, appear to fall short on one or more of these counts.
Since it was first proposed the magnetic levitation of trains has been perceived to offer many potential advantages over conventional train technology. Besides the ability of maglev trains to operate a higher speeds than are deemed possible with wheel-and-rail trains, maglev trains should require less maintenance and be much smoother-riding and quieter than conventional rail systems. These perceived advantages have stimulated major development programs, particularly in Germany and Japan, to solve the technical and economic challenges of this new technology. These decades-long efforts have resulted in impressive demonstration systems, but as yet have not led to commercially operating rail systems in these countries. Factors that have slowed the deployment of high-speed maglev trains based on these technologies include technical complexity and high capital cost.
In an attempt to address these issues by taking advantage of new concepts and new materials, a different approach, called the Inductrack, was proposed. The first-proposed Inductrack disclosed in U.S. Pat. No. 5,722,326, titled xe2x80x9cMagnetic Levitation System For Moving Objectsxe2x80x9d, referred to herein as Inductrack I, employs special arrays of permanent magnets (xe2x80x9cHalbach arraysxe2x80x9d), on the moving train car to produce the levitating magnetic fields. These fields interact with a close-packed ladder-like array of shorted circuits in the xe2x80x9ctrackxe2x80x9d to levitate the train car. In this first form of the Inductrack, single arrays moving above the track produced the levitation. Whereas the Japanese maglev system employs superconducting coils and the German system requires servo-controlled electromagnets for levitation, the Inductrack is based on the use of high-field permanent magnet material, arranged in a special configuration called a Halbach array.
In the Inductrack maglev system Halbach arrays are used, located below the train car. When in motion the magnetic field of these arrays then induces currents in a special xe2x80x9ctrackxe2x80x9d made up of close-packed shorted circuits. Analysis has shown that the combination of the three elements, Halbach arrays, NdFeB magnet material, and close-packed circuits in the track result in the possibility of achieving levitation forces in excess of 40 metric tons per square meter of levitating magnets, corresponding to magnet weights of only a few percent of the levitated weight. The use of Halbach arrays, high-field magnet material and close-packed circuits as employed in the Inductrack thus overcomes previous concerns, e.g., inadequate levitation forces, that led to questioning the practicality of using permanent magnets for maglev trains.
The theoretical analysis of the Inductrack leads to the evaluation of such quantities as the Lift-to-Drag ratio and the levitation power requirements as a function of train speed and of the magnet and track parameters. For the first-proposed, single-Halbach-array, form of the Inductrack, the L/D ratio is given by a simple relationship, given in Equation 1 below.                               Lift          Drag                =                  kv          ⁡                      [                          L              R                        ]                                              (        1        )            
Here k=2xcfx80/xcex, where xcex(m.) is the wavelength of the Halbach array. Note that the Lift/Drag ratio increases linearly with the train velocity and that its slope is determined by the inductance (self plus mutual) and the resistance of the track circuits. For a ladder-like track, that is one composed of transverse bars terminated at both ends with shorting buses, typical values for L and R give Lift/Drag ratios of the order of 300 at speeds of 500 km/hr typical of high-speed maglev trains. This ratio is high enough to make the levitation losses small (less than 10 percent) of the aerodynamic losses at such speeds. Also, for the Inductrack the xe2x80x9ctransition speed,xe2x80x9d the speed at which the lift has risen to half its final value (and also the speed where the lift and drag forces are equal) is low, of order a few meters/second (walking speeds). Thus the first-proposed form of the Inductrack would seem well suited for high-speed maglev train applications.
However, an examination of the first-proposed form of the Inductrack for its possible use in an urban setting, where the typical speeds are of order one-tenth of that of a high-speed maglev system, shows that the older system leaves something to be desired. Now, unless inductive loading of the track circuits is employed, the Lift/Drag ratio will have dropped to 30 or less. For an urban train car weighing, say, 20,000 kilograms, a Lift/Drag ratio of 30 at 50 km/hr corresponds to a drag force of about 6500 Newtons at a drag power in excess of 90 kilowatts.
It is an object of the present invention to provide a track for a magnetic levitation system.
It is another object of the present invention to provide a magnet configuration comprising a pair of Halbach arrays magnetically and structurally connected together and a track located in between such that when the pair of Halbach arrays move along the track and the track is not located at the first plane, a current is induced in the windings and a restoring force is exerted on the pair of Halbach arrays.
It is another object of the invention to attach the Halbach arrays to a vehicle.
An object of the invention is to provide a pair of Halbach arrays that when moving, have a characteristic lift-to-drag ratio at operating loads that can be increased by increasing the area of the pair of Halbach arrays to decrease the downward displacement required to levitate a given weight, and thus decrease the current required for levitation.
These and other objects will be apparent based on the disclosure herein.
The present invention is a track for a magnetic levitation system and incorporates a simple means of inductive loading that distributes the current more nearly uniformly throughout the vertical dimension of the track. In one embodiment, the track is composed of laminated sheets of copper or aluminum that are slotted as shown, with the slots being terminated at their ends to provide a path for the return currents. As also shown, inductive loading of each conductor is provided by including thin strips of ferromagnetic material near the ends of the slots. This inductive loading of each conductor has the additional effect of causing the current to be more evenly distributed within depth into the track, since the currents in each layer are reduced (relative to a track with no inductive loading). This reduction in current diminishes the shielding effect of the currents in the upper layers, thus allowing the vertical component of the field from the Halbach arrays to penetrate throughout the depth of the track. At the same time, the slotting and the use of thin sheets laminated together with insulating material reduces parasitic eddy currents that would otherwise cause extra power losses in the track, reducing its efficiency.
The laminated track, e.g., a track composed of slotted, laminated conducting sheets, is an efficient and cost-effective type of design for the track of Inductrack maglev systems. Its levitation force and its levitation efficiency (lift-to-drag ratio) are greatest when the length of the slots between the shorting sections are minimally wider than the xe2x80x9cfootprintxe2x80x9d of the Halback arrays that comprise the Inducktrack levitation magnet assemblies on the moving vehicle. However, there are circumstances, for example when the track is curved so as to accomplish a change in direction, when the track must be made wider than the transverse dimensions of this footprint, in order to accomplish the turn. Under such circumstances there will be a loss, both of levitation force, and of levitation efficiency. This loss comes about because lengthening the conducting strips increases both their electrical resistance and their inductance. These increases have the effect of increasing the power loss associated with a given levitating current, and at the same time requiring that the levitation gap should decrease so as to maintain the same level of levitating force and/or reducing the levitating force at a fixed levitation gap. The present invention includes a way to design a laminated track so as to minimize the deleterious effects of having slotted regions that are much wider than the footprint of the Halbach arrays.
By leaving unslotted one or more regions between the two unslotted edges of the laminated track, it is possible to define an optimized track region, i.e., one where the length of the current-carrying conductors is minimally wider than the Halbach array footprint, while at the same time providing xe2x80x9cspilloverxe2x80x9d regions that can accommodate lateral excursions of the Halbach arrays associated with tight turns on the guideway. Under such circumstances the Halbach arrays would simultaneously interact with two or more electrically independent track-circuit arrays, each of which would provide a portion of the lifting force. On the other hand, while moving on the straight portions of the guideway, these extra regions would be uncoupled from the inducing fields and thus would contribute no losses, while the central portion of the track would function at maximal efficiency, the length of its conductors being minimally wider than the footprint of the Halbach arrays.
In the present invention, referred to sometimes herein as xe2x80x9cInductrack IIxe2x80x9d, dual arrays are used, one above and one below cantilevered track circuits. Important gains result from the use of dual Halbach arrays: First, the levitating (horizontal) component of the magnetic field is approximately double that of a single array. This circumstance implies that the same levitating force per unit area can be achieved with half the current in the track, i.e., with one-fourth of the resistive power loss. Second, the lower array, when it is phased with respect to the upper array so as to increase the horizontal (levitating) magnetic field component, decreases the vertical field component (the component that excites the current), allowing the optimization of the level of this current. By contrast, in the previous, single array, Inductrack I system the ratio of the vertical field component to the horizontal field component is fixed, so that it is not possible to adjust their ratio. In Inductrack II adjustment of this ratio is accomplished by (i) adjusting the relative gap spacing between the arrays and the track circuits, (ii) or by varying the width of the upper array relative to the lower array and (iii) or by varying the thickness of the lower array relative to the upper array. As a result not only is the levitating power requirement reduced by factors of three or more relative to the earlier Inductrack, but the drag peak, occurring near the lift-off speed, is also reduced by a comparable factor.
Particularly for lower-speed applications of magnetic levitation, such as to urban train systems, it is desirable to employ systems that are simple in construction and operation and that have low drag at urban speeds. Conventional maglev systems, that is, ones employing superconducting coils, or ones requiring servo-controlled electromagnets for levitation, appear to fall short on one or more of these counts. The present invention, an evolutionary development of the Inductrack maglev system, is aimed at providing a solution to this problem. This new system, as with the first-proposed Inductrack, employs special arrays of permanent magnets, xe2x80x9cHalbach arrays,xe2x80x9d on the moving train car to produce the levitating magnetic fields. These fields interact with a close-packed ladder-like array of shorted circuits in the xe2x80x9ctrackxe2x80x9d to levitate the train car. In the first form of the Inductrack single arrays moving above the track produced the levitation. In Inductrack II dual arrays are used, one above and one below cantilevered track circuits. Important gains result from the use of dual Halbach arrays: First, the levitating (substantially horizontal) component of the magnetic field is approximately double that of a single array. This circumstance implies that the same levitating force per unit area can be achieved with half the current in the track, i.e., with one-fourth of the resistive power loss. Second, the lower array, when it is phased with respect to the upper array so as to increase the horizontal (levitating) magnetic field component, decreases the (substantially) vertical field component (the component that excites the current), allowing the optimization of the level of this current. By contrast, in the previous, single array, Inductrack system the ratio of the vertical field component to the horizontal field component is fixed, so that it is not possible to adjust their ratio. In Inductrack II, adjustment of this ratio is accomplished by varying the thickness of the lower arrays relative to the upper array and/or by adjusting the relative gap spacing between the arrays and the track circuits. As a result not only is the levitating power requirement reduced by factors of three or more relative to the earlier Inductrack, but the drag peak, occurring near the lift-off speed, is also reduced by a comparable factor. Theoretical analyses of the Inductrack II configuration and results from computer-based simulations of urban maglev operation will be presented and compared with results for the first-proposed Inductrack system. The present invention is usable for urban speeds (up to 150 kilometers per hour (KPH)) and for high speeds (greater than 150 KPH).
One embodiment of the invention is a magnet configuration comprising a pair of Halbach arrays magnetically and structurally connected together. The Halbach arrays comprise magnet configurations positioned with respect to each other so that a first component of their fields substantially cancels at a first plane between them, and a second component of their fields substantially adds at this first plane. A track of windings is located between the pair of Halbach arrays and a propulsion mechanism is provided for moving the pair of Halbach arrays along the track. When the pair of Halbach arrays move along the track and the track is not located at the first plane, a current is induced in the windings and a restoring force is exerted on the pair of Halbach arrays.